Does mileage really help

Yes. College cross country would be a disaster for you on mpw.

if done properly, you’ll even get faster at 400

It will help a lot.

Yes. And expect even more miles.

It is the number 1 thing that will make you a better runner.

Physiological adaptation takes place through frequency of action/behaviour. Doing something a lot, even if at a lower intensity, will make you much better at that thing.

Let me know how it goes and if the experience was helpful, very interesting.

Nah, non runners are all the fastest runners

It depends what you run the pace at. If you’re always doing 9-10 minute pace it’s not going to get you competitive times. Sometimes you gotta be splitting 6 minute miles and even 5s if you want to train for sub elite. As for 400m , it’s not useless but there are much better ways to train for that

Yeah if you taper for your whole life, then when you do run you will be very fast, but you will never reach that speed ever again

My easy runs are around 7:50-8:20 depending on how I’m feeling and the weather. We have had some runs each week around 7:10-7:20 pace to build our aerobic endurance. I feel stronger, and I don’t think my new coach really cares about my 400 getting faster I may run the 800 at the lowest

It depends what your goals are.

Do you want to be a pure 400 runner?

Do you want to be a 4/800 runner?

Or do you want to be a mid-d runner (800/1500, with the occasional 4X400) who also runs XC?

If your goal is to be a pure 400 runner, I will be a contrarian and say I don't think you need to be running 40+ mpw. You're essentially a sprinter, and it'd be more helpful to focus on plyos, stretching/foam rolling, basic strength in the gym, and of course sprints and some longer intervals. Maybe the occasional "long" run of 3-4 miles too.

400/800 runner, I think 40mpw is fine in the summer, but maybe overkill. You'll want to be doing more stuff like mentioned above as the season approaches.

All around mid-d runner with XC, that sounds right on point for the summer as someone used to running 15mpw.

Since you're new to more mileage, resist the urge to go out and hammer all your runs, that's not the point. Keep your easy runs at no more than 75% max HR, make sure to stretch, ice, and take a day or two off every week. Back off if you feel an overuse injury coming on, it'll save you time and get you fitter in the long term. The idea is to make it to the next day healthy and slightly more calloused to the mileage. You will eventually get used to it, and you'll be amazed at how much faster you are over longer distances.

this. I am most likely never racing the 400 again, I did it in HS because we had better distance runners, I liked the 1600 and ran 5:35 but barely got to race it so I know theirs more I can do. I am getting used to it took about a month. I actually will get close to 45 this week and I’m running 6 days a week with Sunday off.

You seem to be on a good track then. Make sure to incorporate (if not already) core/strength/mobility drills since this is a relatively large jump in mileage.

Overtraining of anything will cause you to get worse at any distance. It takes TIME to adapt to a new regimen.

Yes I definitely don’t want to do that. We are taking Sundays off but my coach is saying if I ever need to take an extra day off here and there its ok and my to take my easy runs easy but I find it’s going well I have a good routine down

5:35 is really good for a girl if you're on 15mpw. 40 mpw will give you plenty of performance uplift. it is also within mileage range that i would say that if you can't run middle distance or XC well on 40 mpw, then 70-100mpw won't do you well either.

I ran all of my best times when I increased mileage.

This is all good advice.

And please ignore the guy who said you need to be running them at a certain pace (he's putting the cart before the horse).

You need to be running your easy mileage at the right intensity, which is between 65-75% max HR. This is commonly referred to as zone 2, which builds mitochondrial function (the energy cells in your muscles), increases capillarisation, improves running economy and also allows you to recover from your easy days. If you run harder than this in between workouts, you'll quickly accumulate fatigue, which is highly likely to cause burn-out or injury.

If you're disciplined, and stick to this intensity though, eventually you'll be able to run 6-7 min/miles at the same HR you currently hold your 8-9 min/miles.

That's not contrarian, nobody who knows what they're talking about is going to advocate 40mpw for the 400. You also never need to do a 3 to 4 mile run. In fact, the general consensus is, if you really want to do a long run, you need to cap it at 20 mins before it starts affecting your fast twitch muscles.

Seems like you’re doing it just right. the paces you’re running, if truly easy, indicate pretty good fitness for someone just starting to train like a distance runner.